Investigate the effector cell sub-populations involved in natural cytotoxicity, the antigens to which this reactivity is directed and the relationship of natural activity to the immune response directed at tumor associated antigens. These studies shall include: Definition of the natural cytotoxic activity of different normal and patient populations with respect to the D-562 model system; effector cell characterization to define further the sub-population of lymphocytes responsible for natural activity in K-562; investigation of the model system antigens and, through the inhibition of cytotoxicity assay, examination of the relationship of the membrane antigens involved in the system to the membrane antigens on cultured cells derived from human tumors; and discrimination of natural cytotoxic activity from the specific reactivity toward putative human tumor associated antigens on the cultured cell lines derived from human tumors by depletion experiments and other means.